1. Field of the Invention
The present invention relates to a phosphorus-copper brazing material and a brazing sheet having a brazing material layer formed of a phosphorus-copper brazing alloy for use in the brazing of parts or members to each other in heat exchangers, electric device components, piping and other such apparatuses. The present invention also relates to a flow path structure for heat exchangers wherein flow path forming members are brazed to each other with such a phosphorus-copper brazing alloy.
2. Description of the Related Art
Members forming flow paths in heat exchangers are formed of Cu (copper) or a Cu alloy including Cu as a major component. Conventionally, such members are brazed to each other with a phosphorus-copper brazing material. According to JIS (Japanese Industry Standards) Z 3264, such a phosphorus-copper brazing material contains 4.8 mass % to 7.5 mass % of P and optionally Ag, the balance consisting of Cu. Since phosphorus-copper brazing materials generally have very poor workability, they are usually supplied in the form of wire, rod or powder. In brazing members of heat exchangers, Ag-free phosphorus-copper brazing materials are generally used because Ag is expensive and might cause a metal allergy in human bodies.
In a brazing operation using a phosphorus-copper brazing material, it is difficult to use the brazing material in the form of rod or power and, hence, the brazing material is preferably in the form of a thin sheet. For this reason Japanese Patent Laid-Open Gazette No. 58-128292, for example, has proposed a phosphorus-copper brazing material exhibiting high cold workability, which is prepared through a process including the steps of: obtaining a crystalline thin strip directly from a molten phosphorus-copper brazing alloy containing P in an amount of 4 wt % to 10 wt % by rapidly cooling and solidifying the molten alloy, and then heat-treating the strip.
However, the preparation of such a phosphorus-copper brazing material requires direct and rapid cooling and solidification of the molten phosphorus-copper brazing alloy, which requires the use of large-scale special production equipment. Further, a special heat treatment is needed to improve the ductility and flexibility of the crystalline thin strip. Therefore, the production cost and the productivity are not satisfactory.
In order to overcome the foregoing problems with conventional methods and devices, preferred embodiments of the present invention provide a brazing material including a phosphorus-copper brazing alloy which can easily be worked into a thin sheet through a cold working process without the need of any special production equipment and any special heat treatment, a brazing sheet having a brazing material layer including such a novel phosphorus-copper brazing alloy, and a flow path structure for heat exchangers including flow path forming members brazed to each other with such a novel phosphorus-copper brazing alloy.
The inventors of the present invention have conducted detailed research on the workability and brazing properties of phosphorus-copper alloys having different P (phosphorus) contents and, as a result, discovered that markedly improved workability can be obtained without sacrificing brazeability when the P content of an alloy falls within a specific range of from about 2.0 mass % to about 3.2 mass %. The present invention has been developed based on this discovery.
According to a preferred embodiment of the present invention, a phosphorus-copper brazing material includes copper as a major component and phosphorus of not less than about 2.0 mass % to not more than about 3.2 mass %, preferably not less than about 2.2 mass % to not more than about 2.9 mass %.
By merely adjusting the P content of a phosphorus-copper alloy so that the P content is within the range of not less than about 2.0 mass % to not more than about 3.2 mass % the alloy is imparted with very high cold workability without deterioration of brazeability.
When the phosphorus-copper brazing material is formed into a thin sheet having a thickness of about 0.01 mm to about 0.15 mm inclusive, the brazing material has excellent brazing operability and very high cost efficiency. Since the phosphorus-copper brazing alloy forming the phosphorus-copper brazing material has excellent cold workability, the thin sheet phosphorus-copper brazing material can simply and easily be manufactured by merely cold-rolling a hot-rolled sheet of the phosphorus-copper brazing alloy into a thin sheet.
According to another preferred embodiment of the present invention, a brazing sheet includes a metal sheet, and a brazing material layer formed integral with the metal sheet on least one side of the metal sheet, the brazing material layer being formed of a phosphorus-copper brazing alloy including copper as a major component and phosphorus of not less than about 2.0 mass % to not more than about 3.2 mass %. The content of phosphorus in the phosphorus-copper brazing alloy preferably ranges not less than about 2.2 mass % to not more than about 2.9 mass %.
In the brazing sheet of this preferred embodiment of the present invention, the brazing material layer formed integral with the metal sheet is formed of the phosphorus-copper brazing alloy having very high cold workability. Hence, when brazing the metal sheet to another metal member, the brazing sheet does not necessitate cumbersome operations including separately providing a brazing material and positioning the brazing material between the metal sheet and the metal member. For this reason, the brazing sheet according to preferred embodiments of the present invention has excellent brazing operability.
If the metal sheet of the brazing sheet is formed of copper or a copper alloy including copper as a major component, improvements are achieved in the pressure weldability between the metal sheet and the brazing material layer and in the productivity of the brazing sheet. Further, an improvement is achieved in the fusion-bonding property, or wettability between the two upon brazing and, hence, such a brazing sheet exhibits superior brazeability.
Since the brazing material layer of the brazing sheet is formed of the phosphorus-copper brazing alloy having superior cold workability, the brazing sheet can simply and easily be manufactured through a process including the steps of: superposing a brazing material sheet formed of a phosphorus-copper brazing alloy on at least one side of a metal substrate, the phosphorus-copper brazing alloy including copper as a major component and phosphorus of not less than about 2.0 mass % to not more than about 3.2 mass %, and cold pressure-welding the brazing material sheet to the metal substrate to form a one-piece sheet in which a brazing material layer reduced from the brazing material sheet is formed integral with a metal sheet reduced from the metal substrate.
According to yet another preferred embodiment of the present invention, a flow path structure for heat exchangers includes a pair of first and second wall members disposed opposite to each other, and a partition member partitioning a flow path disposed between the first and second wall members into a plurality of trickle regions, the partition member being brazed to opposed surfaces of the first and second wall members with a phosphorus-copper brazing alloy including copper as a major component and phosphorus of not less than about 2.0 mass % to not more than about 3.2 mass %.
Since the phosphorus-copper brazing alloy used to form the flow path structure mentioned above includes phosphorus of not less than about 2.0 mass % to not more than about 3.2 mass %, preferably not less than about 2.2 mass % to not more than about 2.9 mass % and hence has very high cold workability, it is possible to attach the phosphorus-copper brazing alloy previously formed into an appropriate shape to each of the opposite surfaces of the first and second wall members before the brazing of the partition member to the wall members. Thus, the operation of brazing the partition member to the wall members can be facilitated, which leads to an improvement in the productivity of heat exchangers.
In this flow path structure, if the first and second wall members and the partition member are formed of copper or a copper alloy including copper as a major component, these members can simply and easily be brazed together via the aforementioned phosphorus-copper brazing alloy and be brazed with superior joining. Further, since copper used as the major component of the members forming the flow path structure is relatively inexpensive, the flow path structure is cost-efficient as a flow path for heat exchangers.
These and other features, elements, steps, characteristics and attendant advantages of the present invention will become apparent from the following detailed description of preferred embodiments thereof when read in conjunction with the accompanying drawings.